There are two problems with these button types; The first is that they seem to attract moisture which can break the connection, this is why the home button on the iPhone 4 can slowly get less responsive over time. Check out this guide to help you diagnose any moisture damage inside the device. Also, to access the home button, check out this home button installation guide. The second is that Apple chose to give the foil part of the button a little nipple like bit which raises it by less than a mm and this sometimes goes wondering around and this makes the external button sit that bit lower and not fully work. The fix for this is to put a tiny 1x1mm bit of 3M tape on the centre of the button and it should work. If this option doesn't release the button then the disk has probably gone flat and you will need a new home button.

Its seems easier to undo the clips on the left and bottom by levering them with an iPad tool and pusing the clips in from the edge with another tool when i can visually see them. One the right side, bottom and most of the left side is done there isnt much need to do the top as it will slide off if moved about a centimeter

I've found that by using a thicker iPad tool dents the back less(not at all if your careful) and start prying just under the volume button and working my way down works better as the metal clips are on all sider except the right side.